Starting seeds can be a tedious and tricky process for many gardeners. Deciding on the proper seed starting mix, selecting containers, monitoring moisture levels and hardening off seedlings are all critical elements in getting seeds off to a good start. However, soil blocking offers a simpler, more foolproof method for starting seeds that eliminates many problems commonly encountered with seed starting.
What is Soil Blocking?
Soil blocking is a seed starting technique that utilizes compressed blocks of soil to start seeds and cuttings. Instead of using traditional containers like flats, pots or six packs, garden soil is compressed into blocks, which creates small compartments perfect for starting seeds. These soil blocks serve as the container and growing medium for seedlings, eliminating any need to transplant. The compressed blocks contain no walls or surfaces that restrict root growth, allowing seedling roots to completely permeate the block.
The History Behind Soil Blocking
Soil blocking originated in European greenhouse production, mainly in Holland, Denmark and Germany. Growers utilized the technique to propagate vegetable starts in the 1980s. At the time, it was common practice to sow seeds in flats filled with peat or other commercial seed starting mixes. Seedlings would grow in the flat until reaching a certain size, then were transplanted into other containers. This process was very labor-intensive and time-consuming.
Representatives from several European tool companies collaborated to design and manufacture simple, handheld devices that could compress soil into blocks with perfectly sized cells for seeds and cuttings. These soil blockers allowed growers to skip the tedious step of transplanting, enabling faster and more streamlined seedling production.
Soil blocking began gaining popularity with small-scale growers in North America in the early 1990s. Master gardener Jim Kennaway launched New Hampshire-based Gardener’s Supply Company in 1983, which was one of the first companies to sell European-made soil blockers in the United States. As more American gardeners discovered soil blocking technology, more variations of soil blockers came onto the market.
Benefits of Starting Seeds in Soil Blocks
There are many advantages to using soil blocks over standard seed starting containers:
No Transplant Shock
Because seeds germinate and grow within the soil block, there are no disturbed roots or other transplant trauma when moving seedlings. Transplanting shock is completely eliminated since the entire soil block gets moved to it’s final growing space.
Superior Root Growth
Root growth is never limited or distorted by smooth surfaces and small containers. Seedling roots fully permeate the block, producing a dense mat of root growth. These robust root systems give seedlings a strong, healthy foundation.
Air Pruning of Roots
As roots reach the outer surface of the block, they stop growing as they become exposed to air. The drying action naturally “prunes” the roots. This prevents roots from encircling the block and promotes increased lateral branching. More roots within the block equates to better growth and resilience.
Less Disease Issues
Starting mixes can sometimes harbor diseases that affect seedlings, especially fungi and molds. The soil blocking technique utilizes real garden soil, which typically contains beneficial microorganisms that keep pathogens in check.
Better Moisture Control
The soil mix used for blocking retains moisture well and blocks rarely dry out completely. Seeds germinate easily without constant monitoring of moisture like other seed starting systems may require. At the same time, blocks provide good drainage and aeration.
Adaptability & Customization
Gardeners can create blocks in an array of sizes to accommodate all types of seeds and cuttings. Specialized blockers allow for endless variations in block sizes and configurations. Seeds and seedlings with specific needs can be accommodated.
Direct Seeding into Garden Spaces
The ultimate goal is to move seedlings in blocks directly into the garden bed, establishment container or cell pack. By eliminating any transplanting or root disturbance, plants experience almost no setback in growth. This makes soil blocking ideal for crops that dislike having their roots disturbed, like celery, peppers, eggplants or melons.
Less Plastic Waste & Expense
Most seed starting containers and trays are made of plastic and get discarded after one or two uses. With a soil blocker, there is no ongoing cost or waste created since blocks are made of garden soil. A single soil block maker can last many seasons.
Takes up Less Space
Instead of shelves full of seed trays and flats, seeds can be started in a smaller concentrated area with block trays holding dozens of blocks. Space requirements are cut drastically with the soil blocking system.
Getting Started with Soil Blocking
While soil blocking might sound a bit complex, it’s actually simple to incorporate into seed starting routines. Follow these basic steps to begin making and using soil blocks:
Choose a Soil Mix
Almost any decent potting mix can be used for blocking but ideally one that contains compost or leaf mold. These organic components help blocks retain moisture and give stability. Pre-mixed blends labeled specifically for soil blocking are also available from some garden suppliers.
Avoid any mixes with synthetic fertilizers or excessive peat moss, as they can inhibit good compression when blocking. The best mixes contain compost, coir or coco fiber, vermiculite or perlite and a small amount of good organic potting soil.
Before compressing soil into blocks, water must be added so that the mix sticks together. As a general rule, add water equal to 20-30% of the volume. For example, 5 quarts of soil mix would require 1 to 1.5 quarts of water added. Stir the water well into the entire batch of soil so it’s uniformly moistened. Test compression by squeezing a handful of soil. If it holds together in a ball without crumbling apart, it has the proper moisture content.
Prepare Blocker & Trays
Select the appropriately sized blocker for the seeds or plants being started. Line trays with plastic wrap or a moisture retention mat that blocks will sit upon. These help retain moisture so the bottoms of blocks do not dry out.
Compress Soil into Blocks
Open up the chamber in the soil blocker and fill it completely with the moistened soil mix. Close the lid and press the top and bottom together using firm pressure. This compresses the soil into the block cavities. Open up the chamber and gently tap out the newly formed blocks onto the tray. Leave an inch or so between blocks to allow seedlings adequate space.
Sow Seeds & Label
Most soil blockers come with small dibble sticks or tampers that create perfect indentations in the block surface for placing seeds or seedlings. Sow 1 to 2 seeds per block cavity. Lightly cover them with a pinch more soil or vermiculite if required. Label trays with the variety and date sown.
Water Blocks & Cover
Water the blocks well from overhead after sowing so the entire block is moistened again. Place a seedling heat mat under the trays if needed. Cover trays with plastic dome lids or baggies to retain humidity during germination.
Grow Seedlings & Harden Off
Care for seedlings in blocks the same as any other method, keeping adequately watered and providing warmth/light as needed. Slowly introduce blocks to outdoor conditions over 7-14 days (hardening off) before transplanting.
Tips for Success with Soil Blocking
Like any gardening technique, there is a learning curve with soil blocking. With a little practice using an appropriate soil mix, gardeners can successfully utilize this method. Here are some helpful pointers:
- Make sure the soil mix used is not too dense or fine textured. A mix with vermiculite, coconut coir and compost contains enough air pockets for easy compression.
- Getting the moisture level perfect when preparing soil is key so blocks hold their form well. Soil that is too dry or too wet will not compress properly.
- Fill blocker chambers heaping full and tamp soil down well before compressing to reduce air pockets.
- Gently ejecting new blocks onto trays is better than trying to force them out, which risks crumbling edges.
- Allow blocks a day or so to fully dry and set up before sowing seeds. Slow drying also helps them retain their shape better.
- Water mature blocks from the bottom tray rather than overhead to avoid disturbing newly placed seeds or erosion of block sides.
Soil Blocking Tools & Equipment
Gardeners have a vast array of soil blockers to pick from, ranging from basic handheld units to automated systems:
Manual Soil Blockers
Easy-to-operate basic blockers like the original Soil Blocker allow gardeners to make 4 or 8 blocks at a time. Manual units like the Ultimate Soil Blocker have interchangeable block forming parts to make blocks from tiny up to jumbo sizes. Most manual blockers have a pressure lever that compresses soil into blocks with each squeeze.
Power Soil Blockers
Power soil blockers utilize electric, battery-powered or lever-activated pistons to generate the heavy pressure needed for compression. Minimal physical exertion is required compared to standard manual versions. Commercial growers often employ heavy-duty power block cutters mounted to workbenches, which churn out blocks on an industrial scale.
Soil Block Making Machines
At the high end of soil blocking equipment are automated, power-driven block making machines. Units like the Soil Block Making Machine have chambers that automatically fill with soil, get compressed into uniform blocks, then eject the finished blocks in one smooth process. Programmable settings allow customization of block sizes and shapes.
A variety of supplementary products help streamline soil blocking:
- Dibble sticks for indenting block surfaces to plant seeds
- Special trays fitted for holding blocks
- High dome propagators create mini-greenhouses over block trays
- Heated propagation mats for under trays
- Label presses or markers for labeling
- Precision seed sowers or vacuum seeders
Soil Blocking Various Crop Types
One of the advances of soil blocking technology is the ability to customize blocks for specific crops. Not all seeds and plants are started the same way, so soil blocking has adapted to accommodate these differences.
Small Seeded Crops
Tiny seeds like lettuce, kale, carrots, leeks can be tricky to handle individually. Vacuum seeders or automated seeders make sowing fuss-free. Cover blocks with vermiculite after planting to maintain ample moisture for germination. Dome lids help retain humidity.
Large Seeded Crops
Larger seeds like beans, corn and peas are easy to hand sow, 2-3 seeds per block. Quickly emerging seedlings like these often outgrow small blocks rapidly. Jumbo block sizes help alleviate crowding of root systems.
Tomatoes & Solanaceae Crops
Getting a head start on warm season veggies is where soil blocking excels. Germinating tomatoes, peppers and eggplants in blocks avoids transplant shock when installed in the garden. These seedlings appreciate wider, deeper trays that give roots extra room.
Herbs & Flowers
Since most herbs spread out instead of growing deep roots, standard or petite block sizes suffice. Pelleted seeds simplify planting herbs like parsley, basil or cilantro. Flower varieties can be color coded into block rows for easier tracking.
Perennials, Shrubs & Trees
Soil blocks enable gardeners to inexpensively propagate all kinds of perennials from seed. Long taproots on perennials like hollyhocks are uninhibited by blocks. Blocks can also function as starter pots for shrubs, trees, roses and any plant that dislikes root disturbance upon transplanting.
Getting Soil Blocks Off to a Great Start
Proper care right after seeding is crucial to aid in germination and support young seedlings. Follow these tips:
Create a Mini-Greenhouse
Enclose seeded block trays in plastic tunnel greenhouses or under humidity dome lids. This keeps the environment uniformly warm, moist and well-ventilated until sprouts push through the soil blocks.
Bottom Heat is Beneficial
Many plants appreciate gentle bottom heat from below to spur germination.Propagation mats under block trays regulate temperatures perfectly. Thermostats prevent overheating while warming roots by 10-20 °F.
Light is Essential, Even for Germination
While darkness suits some seeds when sprouting, most benefit from immediate exposure to light. Place seeded blocks under grow lights turned on 12-16 hours daily. Adjust lights as seedlings stretch upwards.
Air Circulation & Ventilation
As soon as tiny seed leaves open, crack lids or remove tunnel covers to allow air movement. Have a small fan circulate air around block trays to toughen stems and prevent disease.
Once established, begin weekly fertilizing with 1⁄4 strength organic liquid fertilizer like fish emulsion or compost tea. This prevents nutrient deficiencies but doesn’t force seedlings. Stop fertilizing 2 weeks before transplanting.
Hardening Off Soil Blocks
The week or two before transplanting soil blocks into the garden is vital for proper hardening off. This gradual introduction to real world growing conditions minimizes any setbacks after transfer.
Phase-In Outdoor Conditions
Start by moving block trays outside to shaded, protected areas for a few hours daily. Time spent outdoors should increase gradually over 7-14 days. Bring seedlings back indoors if conditions become harsh.
Allow Wind and Sun Exposure
Place block trays in increasingly sunny spots so plants adapt to more intense light levels. Minimal wind training toughens cell walls in stems and leaves over time. Monitor for any stress signs like wilting or purpling.
Adjust Watering Frequency
Plants lose moisture quicker outdoors, so check blocks more often for water needs. Allow the soil surface to partly dry out between waterings. Going into transplanting, drier blocks are easier to handle without damage.
Hold Off Fertilizing
Stop liquid feeding once the hardening off process starts so seedlings channel energy into root production rather than excessive top growth. This helps prevent transplant shock.
Transplanting Soil Blocks
The payoff for all the care given to soil blocks is how seamlessly they transition into garden beds or other containers. There are no disturbed roots to recover from so plants take right off with exponential growth.
Select Transplant Sites
Prepare permanent garden beds or containers before installing blocks. Amend soil generously with compost and organic fertilizer. Identify spots suited to each variety’s mature size and needs like sunlight or drainage.
Water Blocks Well Before Transplanting
Plants should never enter new environments overly dry. Water blocks thoroughly a day prior to transplanting so they are moist but not saturated. Saturated blocks are heavy and delicate to handle.
Handle Blocks Gently
Carefully lift or slide blocks using slotted spatulas or the block tray itself for support underneath blocks. Never tug seedlings right out of blocks. Guide roots into holes or spaced openings.
Plant Blocks at Same Level
When transplanting blocks into garden beds, make sure the soil level matches previous height in trays. Keep the upper portion of blocks right at ground level so plants experience no burying or exposure of stems.
Water & Monitor Establishment
After getting blocks settled into spaces, water gently to moisten surrounding root zones. Overhead water right onto blocks may erode sides before plants root out. Check soil moisture daily as plants establish over the first weeks.
Troubleshooting Common Soil Block Problems
When just getting started with the soil blocking method, some potential problems can come up:
Blocks Won’t Release from the Chamber
- Spray inside surfaces very lightly with nonstick pan spray so soil does not stick to surfaces.
- Ensure chamber parts are completely clean and soil is not caked on.
Block Shape is Irregular
- Evaluate soil mix and moisture content. A coarse, sandy or dry mix can prevent uniform compression.
- Check that the blocker chamber fills completely before compressing and soil is distributed evenly.
Blocks are too Dense or Heavy
- Use a soil mix containing vermiculite or perlite to create more air pockets and lighter blocks.
- Avoid pressing block makers too firmly together and compress just enough for blocks to cleanly release.
Blocks are Cracking Upon Handling
- Let blocks fully dry for 48 hours after forming so the soil particles adhere firmly.
- Mix may be too wet, creating weakness in block structure. Test moisture before adding water.
Seeds/Seedlings have Poor Survival
- Ensure blocks do not dry out for the first few days after sowing seeds. Bottom heat below the trays can also boost germination.
- Fertilize blocks lightly with a balanced organic fertilizer once the first true leaves emerge.
Pros and Cons
- No transplant shock or disturbance of seedling roots
- Roots grow freely without restricting surfaces
- Air pruning of roots promotes dense root growth
- Less damping off disease
- Excellent moisture retention properties
- Customizable block sizes for any seed or plant
- Space efficient trays and setup
- Reusable soil mix instead of waste from containers and flats
- Very economical long-term
- Higher initial investment in blockers and accessories
- Learning curve to master soil moisture levels and technique
- Must be diligent about labeling blocks
- Not as much variability in block sizes and shapes as traditional pots/cells
- Lack of nutrients over time if not supplemented
- Blocks may be difficult to properly harden off
- Handling dozens of loose blocks can be unwieldy
Soil Blocking is Simple & Effective
While traditional seed starting has worked for generations, soil blocking brings ease, efficiency and ecological benefits to propagation. This innovative technique eliminates transplant shock, yields robust seedlings with vibrant root systems and consolidates space requirements for starting seeds. With a small investment in equipment and some practice, soil blocking can transform any gardener’s seed starting struggles into smooth, thriving germination success.
Most soil blocks decompose naturally over time, lasting 2-3 months on average. However, some sturdier blocks may hold form for 4-6 months. Block longevity depends on soil mix and compaction quality.
Yes, it’s possible to start seeds too far in advance with blocks just like any propagation method. Grow the shortest season varieties first, then progress to longer season types as transplant timing approaches.
Warmth accelerates germination with blocks. Use heating mats or cables under block trays set to 70-75°F. Or place trays above appliances like refrigerators that emit warmth.
Yes, bottom heat that gently warms roots is ideal and avoids drying out block surfaces quickly. Use grow lights overhead to provide additional warmth if needed.
No. Keep grow lights 4-6 inches above block trays to prevent drying blocks out. Lightly fertilize blocks if seedlings become leggy reaching for light.
Set blocks outdoors daily to slowly adjust to sunlight, wind and weather changes for 7-14 days pre-transplanting. Protect from extreme sun/heat and provide ventilation.
In most cases, no. Stacking standard block trays risks damaging tender roots emerging from lower block layers. However, some specialized block systems have tiered vertical designs allowing stacking.
As the myriad benefits of soil blocking come to light each year, more and more growers are adopting this innovative propagation technique. No longer confined mainly to commercial greenhouse production, soil blocking has hit the mainstream and captured the interest of home gardeners, urban farmers, preppers and anyone wanting to grow their own food.
Beyond just being a novel concept, soil blocking delivers tangible advantages over traditional seed starting methods that frugal and eco-minded gardeners can no longer ignore. The prospect of reducing plastic waste, saving money and enjoying healthier transplants year after year makes soil blocking a wise investment.